Our hypothesis is that asbestos and SV40 are co-carcinogens in causing malignant mesothelioma (MM). This hypothesis is based on in vitro experiments using human mesothelial cells (HM) and in vivo experiments in hamsters. We found that neither asbestos nor SV40 small t antigen mutants could cause HM malignant transformation. However, when HM were exposed to both asbestos and SV40 small t mutants, malignant transformation and focus formation occurred. Moreover, preliminary results demonstrated a potent co-carcinogenic effect in hamsters coinjected with SV40 small t mutant intracardially and with asbestos intrapleurally and intraperitoneally. Our findings suggest that individuals exposed to both asbestos and SV40 are at increased risk of developing mesothelioma. Here we want to study the mechanisms of co-carcinogenesis. We propose to conduct these studies in human and in hamster mesothelial cells in tissue culture, and in hamster and human mesothelioma biopsies. In Aim 1 we will determine the biological effect of TNF-alpha, PDGF and TGF- beta in SV40-asbestos co-carcinogenesis in HM in tissue culture. In preliminary results we found that our mesothelial cells express receptors for these cytokines. We also found that TNF-alpha expression and receptor are induced in HM following asbestos exposure or SV40 infection. HM exposure to TNF-alpha induced NF-kbeta activation which plays an important role in oncogenesis. In parallel we are studying the effect of SV40 and asbestos on the Ras-ERK pathways and AP-1 induction, because we found that both, SV40 and asbestos induce ERK1/2 and downstream effectors in HM in tissue culture. Our hypothesis is that all these mechanisms are inter-related and we will study the biological significance of these mechanisms in SV40-asbestos co-carcinogenesis. In Aim 2A, the same cytokines and gene pathways studied in Aim 1, will be investigated in frozen specimens from MM we induced in hamster with asbestos, SV40, and SV40 small t mutant plus asbestos, and the results compared. By comparing the in vitro data (aim I), with those produced in an experimental MM model (Aim 2A) in which exposure, was under our control, we will identify among many possible candidate gene pathways, those that are most relevant to MM pathogenesis and to SV40-asbestos pathogenesis and co-carcinogenesis. The results will be validated by studying the same cytokines and gene pathways identified in vitro (Aim 1) and in hamster MM (aim 2A) in a unique collection of 38 frozen MM biopsies and matching lung tissue (Aim 2B). In these 38 samples we have determined SV40 status and type and amount of asbestos exposure. Finally, in Aim 3 we will attempt to establish an SV40-asbestos mouse tumor model, similar to the one we established in hasmters. The availability of a mouse model would be ideal for future mechanistic and experimental therapeutic approaches because of the large number of mouse reagents (monoclonals, transgenic mice, knock-out mice, etc.). It is anticipated that the results of the experimens proposed in this application will provide information to design novel preventive and therapeutic approaches for MM.